Plier type toggle wrenches have long been utilized in the prior art. Most of these wrenches have commonly employed a toggle mechanism so designed as to pass over a dead center position for locking a pair of gripping jaws in clamped engagement with a workpiece. Such wrenches normally include an adjusting mechanism to adjust the distance between the gripping jaws, thereby permitting the jaws to grip workpieces of different sizes and shapes. The adjusting mechanism further serves as an adjustment of the gripping force exerted by the jaws.
These prior art wrenches, which are locked onto the workpiece when an element of the toggle mechanism passes beyond or over toggle dead center, are released or opened either by pulling apart the operating handles manually, or by actuating a control lever so as to break the toggle apart. When maximum mechanical advantage of the toggle is employed to clamp a workpiece between a pair of gripping jaws, it is very likely to have the handles come apart very rapidly and with considerable force when the toggle is broken. A large toggle wrench of this type must be treated with respect as a dangerous tool because of the sudden release of energy. The casual user of such a toggle wrench can easily be struck in an eye or break a tooth when the wrench flies open upon release.
It is also known in the art to employ wrenches having toggle mechanisms which are adjustable so that the elbow of the toggle does not pass over or beyond the toggle center line. Such wrenches should be adjusted to exert the maximum gripping force just prior to the elbow of the toggle reaching the toggle center line.
The best known prior art toggle wrench of this type is Petersen, U.S. Pat. No. 2,853,910 Latch Means For Plier Type Toggle Wrench. This patent teaches a wrench which includes a toggle mechanism comprising an actuating lever 21 and a link 23. A latch bar 30 is provided and is pivotally mounted to the actuating lever 21. The latch bar 30 includes a hook-shaped latch 33 which, when engaged with a latch engaging lip 36 on the link 23, securely latches the jaws 11 and 13 in a gripping position. The latch bar 30 is further provided with a finger engaging portion 37 which serves, when depressed, to release the toggle mechanism and permits the jaws 11 and 13 to open under the action of a tension spring 16. This wrench has been found to be very difficult to manipulate because the finger engaging portion 37 is not positioned to be in an easily accessible location. For this reason, most operators must use both hands to operate the wrench, one for holding the tool, and the other for operating the latch.
There is a need for an improved plier type toggle wrench which includes a toggle mechanism which operates to close the jaws of the wrench in a clamping position just prior to reaching the toggle dead center position and which includes a readily accessible release button positioned so as to enable a user to control the tool easily with one hand.